Income Taxes (Tables)

12 Months Ended

Dec. 31, 2013

Income Taxes

Schedule of reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations

A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows (in thousands):

	Year Ended December 31,
	2013			2012			2011
Income tax benefit using U.S. federal statutory rate	$	(20,635	)	$	(23,504	)	$	(14,509	)
State income taxes, net of federal benefit		(2,255	)		(2,774	)		(1,854	)
Stock-based compensation		92			72			49
Research and development tax credits		(1,277	)		(55	)		(385	)
Change in the valuation allowance		27,194			25,175			17,041
Permanent items		(3,085	)		709			91
Other		(34	)		377			(433	)
	$	—		$	—		$	—

Schedule of principal components of the Company's deferred tax assets

The principal components of the Company's deferred tax assets are as follows (in thousands):

	December 31,
	2013			2012
Current assets:
Accrued expenses	$	351		$	343
Deferred Rent		9			—
Gross current deferred tax assets		360			343
Valuation allowance		(360	)		(343	)
Net current deferred tax assets	$	—		$	—
Non-current assets:
Net operating loss carryforwards	$	100,284		$	74,487
Capitalized research and development		662			1,042
Research and development credits		4,345			3,067
Depreciation and amortization		110			90
Other		1,313			851
Gross non-current deferred tax assets		106,714			79,537
Valuation allowance		(106,714	)		(79,537	)
Net non-current deferred tax assets	$	—		$	—